1. Field of the Invention
The invention relates to a capacitor component for mounting on a component assembly carrier provided with electronic circuit elements, to the component assembly carrier and to a method of making the capacitor component, in order to provide a plurality of capacitors with precisely matched capacitances.
2. Description of the Related Art
One such capacitor component is known for instance from U.S. Pat. No. 5,034,850 and includes a ceramic plate onto which a first electrode layer is applied. Applied to the first electrode layer is a thin dielectric layer, followed by a second electrode layer. The terminals of the electrode layer are extended laterally out of the component and are carried to the underside of the ceramic plate by means of conductors applied to the face ends of the capacitor component. Such capacitor components are mounted as discrete capacitive components, for instance onto printed circuit boards, and are soldered to the conductor tracks present there. Not only is the complicated design of the terminals, which makes producing such capacitor components relatively expensive, a disadvantage, but moreover the capacitances of two identically designed capacitor components, each of which includes a single capacitor, can deviate sharply from one another.
The reasons for this can be found in the tolerances in the production of the components. The applied electrode layers can fluctuate from one time to another in their thickness and surface area. Furthermore, fluctuations in thickness of the dielectric layer employed and a variable offset of the upper and lower capacitor electrodes in production lead to different capacitances of the components produced. For these reasons, the known capacitor components cannot be used in all electronic circuits. Especially for electronic bridge circuits, in which capacitors whose capacitances match as precisely as possible must be used, the known capacitor components are unsuitable.
It is an object of the present invention to provide a capacitor component with at least two capacitors having precisely matched capacitances and a component assembly carrier with the capacitor component mounted on it and with electronic elements connected electrically with the at least two capacitors.
It is another object of the present invention to provide a method of making the capacitor component with at least two capacitors having precisely matched or identical capacitances.
According to the invention the capacitor component comprises at least two capacitors including a first and second capacitor and a common dielectric substrate plate. The first capacitor has a first electrode layer on a top side of the dielectric substrate plate and a second electrode layer on an underside of the dielectric substrate plate opposite from the first electrode layer. The second capacitor correspondingly has a third electrode layer on the top side of the dielectric substrate plate and a fourth electrode layer arranged on the underside of the dielectric substrate plate opposite from the third electrode layer. The third electrode layer has spatial dimensions corresponding to those of the first electrode layer, and the fourth electrode layer has spatial dimensions corresponding to those of the second electrode layer, whereby the capacitors have precisely matched capacitances.
In the method of making the capacitor component, the first and third electrode layers are applied at the same time to top side of the dielectric substrate plate and the second and fourth electrode layers are applied at the same time to the underside of the dielectric substrate plate.
With the capacitor component according to the present invention, the disadvantages known from the prior art are avoided. The capacitor component of the invention has at least two identically constructed capacitors, whose dielectric layer is formed by the same dielectric substrate plate. Since the electrodes on the top and bottom sides of the dielectric substrate plate are made on the same substrate in the same production process, an offset between the upper and lower electrode layers, or a deviation in the thickness of the electrode layers resulting from fluctuations in quantity upon the application of material, always affect the. magnitude of the capacitances of the two capacitors to the same extent. The relative deviations in capacitance thus always remain very small. Another advantage is the simplified structure of the capacitor component, comprising a dielectric layer provided with electrode layers on the top and bottom sides, which dielectric layer at the same time serves as a carrier plate. This makes it unnecessary to provide a separate carrier for mechanically stabilizing the capacitor structures, as is needed in U.S. Pat. No. 5,034,850.
Refinements of the invention and advantageous embodiments are made possible by the characteristics recited in the dependent claims.
Advantageously, a ceramic plate is provided as the dielectric substrate plate. Such plates can easily and inexpensively be produced with high precision.
Advantageously, the electrode layers are applied to the dielectric substrate plate by thick-film or thin-film technology.
Preferably, the procedure is such that the first and third electrode layers are applied in a common method step to the top side of the carrier plate, and the second and fourth electrode layers are applied to the underside, also in a common method step, under the same process conditions, to the dielectric substrate plate. As a result, electrode layers with geometric dimensions that deviate only extremely slightly from one another can advantageously be created on one side of the carrier plate. Thus the capacitors formed in the capacitor component all have the same capacitance.
Advantageously, the capacitor component can be mounted as a discrete component onto a component assembly carrier and contacted electrically and mechanically to conductor tracks located there, for instance by reflow soldering. The electrode layers present on the top side of the capacitor component are contacted to further conductor tracks of the component assembly carrier via bond wires. Thus the capacitor component can be mounted relatively simply and inexpensively, by well-mastered techniques.